This invention is directed to the synthesis of hydrated alkali metal silicate ion-exchange material in the form of white crystals using discolored iron-contaminated naturally occurring kaolin clay as a source of alumina and silica.
There is currently interest in using certain sodium aluminosilicate ion-exchange materials in detergent compositions. Reference is made to Belgian Pat. No. 814,874 to Corkell et al. The preferred sodium aluminosilicate ion-exchange material has the formula Na.sub.12 (AlO.sub.2.SiO.sub. 2).sub.12.27 H.sub.2 0 which corresponds to the formula of sodium zeolite A as described in U.S. Pat. No. 2,882,243 to Milton. The ion-exchange builder material may be produced, according to the Belgian patent, from high purity sodium aluminate, sodium silicate, sodium hydroxide and water. It is well known that zeolitic aluminosilicates such as sodium zeolite A can be obtained at relatively low cost by using minerals as sources of silica and/or alumina. Kaolin clay calcined to the so-called "metakaolin" state or condition is an example and it is useful when reacted with sodium hydroxide solution as the source of both silica and alumina in the production of zeolite A. Obviously a sodium aluminosilicate product used as a builder in a washing composition intended for consumer use must have a white, bright appearance in order to satisfy aesthetic demands.